Dr. Manuel de Costa, Associate Director, Outcomes Research with Zoetis, recently spoke to The Poultry Site’s Sarah Mikesell at the 2023 IPPE in Atlanta, Georgia, USA.

Live vaccine for Salmonella and E. coli

“Salmonella and E. coli are diseases that are very impactful to poultry production,” said Dr. Da Costa. “Salmonella is especially impactful on the food safety side. As an industry, we need to guarantee to provide the best product to our consumers.”

Escherichia coli impacts the performance side usually in long-lived birds, but it can also affect broilers.

That’s where live bacterial vaccines come in, specifically, live Salmonella Typhimurium and live E. coli vaccines, according to Dr. Da Costa. Both vaccine products are mass applied usually via spray or drinking water. They share a common technology of attenuation by deletion of the aroA gene.

“When these vaccines are given, the birds are exposing their immune system to the bacteria and mount a cellular immune response,” said Dr. Da Costa. “The aroA gene deletion makes these bacteria very sensitive to the environment so they don’t persist, but it also makes them very susceptible to processing by the immune system. What we're doing is basically allowing the birds to adaptively respond to these two challenges in the field.”

Is cross protection an important trait?

Both Salmonella and E. coli have different colors and shapes.

“If you think about Salmonella, the vaccine is for a Typhimurium strain,” said Dr. Da Costa. “When you look at the processing plant’s FSIS data, you can see Kentucky coming in, and Infantis is an extremely important serotype along with Heidelberg and Enteritidis.”

Having a vaccine that can not only protect against a specific serotype but can touch all of these other strains from the same family is extremely important.

“Here at IPPE, we had the International Poultry Scientific Forum, and there were some presentations on populations of E. coli,” he said. “One of the most prevalent serotypes of E. coli is O78, but there’s an array of other E. coli strains, like O2 and O25 that are present in our environment. Having vaccines that can work not only against the O78 serotypes but on other serotypes is very important to the poultry industry.”

Over the last few years, Zoetis has been running live vaccine trials to measure live ST’s ability to help reduce Salmonella in poultry.

“There's a similar aroA attenuated live ST vaccine licensed in Australia. This vaccine has a claim for Salmonella Typhimurium in addition to a claim for Salmonella Infantis,” he said. “Boosting via intramuscular administration has demonstrated protection for up to 65 weeks of age against Salmonella Infantis—so it provides long-lived protection and cross protection which is very important.”

This study triggered Zoetis’ interest, so they started to explore and run trials to evaluate the feasibility of the strategy.

“We wanted to make sure that it was an easy solution,” he said. “We evaluated combinations of the live vaccines with inactivated products because we wanted to have the least manipulation of the birds and injections. You want to keep it simple. We observed that when you combine with an inactivated SE-ND-IB vaccine \ products were compatible.”

Zoetis ran a few in vivo trials and learned that when you administer the vaccines intramuscularly, the birds get further protection compared to the conventional route by mass application. For example, for Salmonella Heidelberg and Salmonella Enteritidis, the protection was a little bit different than with the mucosal application.

“When live ST vaccines are given conventionally, you expect a mucosal response, but when it was injected intramuscularly, the response also triggered a humoral (antibody) response. Salmonella is usually present in the ceca, and when the vaccine was applied by mass spray or water, you had a reduction,” he explained. “When we tested the parenteral (injection) application, we saw similar reductions in the cecal loads but saw even greater reductions in the internal organs including reproductive tracts.”

Vaccine results for E. coli

“The results of the E. coli vaccine were similar to those of Salmonella,” he said. “We had data that we generated many years ago of live E. coli that was effective given parenterally. We piggybacked on the success of the Salmonella studies. by combining it with inactivated SE-ND-IB vaccine, and they were again compatible.”

Zoetis then conducted more testing through bird trials, comparing intramuscular injection with a conventional application by mucosal administration.

“What we observed was the eye drop application usually did a good job reducing both mortality and disease susceptibility against avian pathogenic E. coli (APEC). Our challenge model was with the O78 serotype,” said Dr. Da Costa. “But when we looked into the final results in terms of air sac lesions, perihepatitis and pericarditis, the intramuscular application really reduced the lesions, and it gave ‘a little bit extra’ when compared to the eyedrop treatment. And when an overwhelming APEC challenge dose (10^10 CFU/bird) was given, only the injection treatment still significantly reduced both mortality and internal lesions.”

Another interesting finding occurred in a trial where we compared injecting the live E. coli by itself to combining it with the inactivated SE-ND-IB product.

“When we gave a combination of both, mixing them in the same bottle, this gave a numerically improved response over giving the live E. coli by separate injection. What we think we learned is when you mix both products together, you actually get a little bit more immune response and we think that is related to the adjuvant effect of the inactivated vaccine,” said Dr. Da Costa.” You can get an even better immune response to the live E. coli injection when it’s presented to the bird along with the inactivated vaccine.”